the fbi says agents searched dzhokhar tsarnaev's college dorm room and found bbs and what they call a large pyrotechnic. they also say they found a white hat and black jacket resembling what was worn in the photos released by the fbi. a former federal prosecutor says it's a surprisingly solid start. >> they took a great unknown, which was last monday, and made it virtually unknown just a week later. and the entirety of the law enforcement that worked this case should be commended for their efforts. >> reporter: court documents also contain new details about thursday night's carjacking. the fbi says surveillance pictures show dzhokhar and tamerlan tsarnaev at a gas station in cambridge where they drove with the owner of the suv they carjacked. one of them, investigators say, began the carjacking by pointing a gun at the driver and saying, "did you hear about the boston explosion? i did that." the carjacker showed the driver that he had bullets in his gun according to the fbi and said, "i'm serious." at the scene of the shootout in watertown where tamerlan tsarnaev was killed, other exp